1. College of Mathematical Sciences, Inner Mongolia Minzu University, Tongliao 028043, China
2. Department of Mathematics, National Kaohsiung Normal University, Kaohsiung 82444, Taiwan
3. School of Mathematics and Physics, Hulunbuir University, Hulunbuir 021008, China
4. School of Mathematics and Informatics, Henan Polytechnic University, Jiaozuo 454010, China
5. Independent Researcher, Dallas, TX 75252-8024, USA